1. Field of the Invention
The present invention relates to a color interpolation apparatus for determining color values of pixels of a bayer pattern inputted from a single image sensor and, more particularly, to a color interpolation apparatus capable of accurately interpolating color of pixels in consideration of various directionalities of edge components of an image.
2. Description of the Related Art
In general, a digital camera, a camcorder, a camera phone, and the like, generates images by using an image sensor such as a charge coupled device (CCD), a complementary metal-oxide semiconductor (CMOS), and the like. The image sensor receives light via a photodiode or a photo transistor, generates an electrical signal according to the received light, converts the electrical signal into an electrical digital image signal by using an analog/digital converter, and outputs the converted signal.
A color image can be expressed with at least three colors of green, red, blue, the three primary color elements, at each pixel. Thus, in order to display a color image, three image sensors plus color filters for receiving each color and driving circuits for driving each sensor are required. For example, a broadcast equipment, a high-performance camera, etc. expresses a color image by using three image sensors. However, most digital cameras and camera phones express a color image by using a single image sensor to reduce the size and costs. The image sensor has a function of converting a signal of light into an electrical signal, and the signal inputted from the image sensor is a black and white image with only brightness information of a subject, not a color image. Thus, in order to express a color image by using the single image sensor, the image sensor needs a special filter arrangement called a color filter array (CFA). Among color filter arrays, a color filter array of a bayer pattern is the most commonly used color filter array. With the color filter array of the bayer pattern, a single pixel can obtain only single color information, and the pattern includes red-green repeated rows and green-blue repeated rows which are alternately disposed repeatedly. When the color filter array of such bayer pattern is in use, a bayer pattern image with pixels each having only one color information of the three red, green, and blue colors is outputted. Thus, in order to obtain a complete color image, a process of recovering the other two remaining color information a corresponding pixel does not have by using the color information of the corresponding pixel and color information of its neighbor pixels is required. The process of generating the color image by recovering the three color information with respect to each pixel of the bayer pattern image outputted from the image sensor is called color interpolation or demosaicking.
Various researches have been conducted so far on the color interpolation scheme, and diverse color interpolation methods have been known, including a method of simply interpolating color with an average value of color values of neighbor pixels and a color interpolation method of applying various algorithms according to the presence or absence of an edge and the directionality of an edge. The color interpolation scheme may be applicable in various manners depending on diverse elements such as the directionality of an edge present in an image to be color-interpolated, the luminance of the image, a type of an image sensor, and the like, and in this sense, research and development of the color interpolation scheme needs to be continued.